The flag of the losing side of the U.S. Civil War -- a symbol that many Americans consider racist -- is at the heart of a complex free speech case that opened Monday at the Supreme Court.

A group known as Sons of Confederate Veterans wanted the old flag of the Confederacy -- a blue X containing stars on a red field -- to be an optional logo on motor vehicle license plates in Texas.

Many U.S. states allow motorists to add images and slogans that express deeply held views. And they bring in sizable revenues for state coffers: $17.6 million last year in Texas alone, where they cost about $30 apiece.

But the Confederate flag represented a major secessionist battle to preserve slavery in the 1860-64 war, which killed more than 600,000 people. The symbol continues to be used by many white supremacist groups.

After receiving numerous protests against the license plate, the Texas state board of motor vehicles denied the request, arguing that “a significant portion of the public associate the confederate flag with organizations advocating expressions of hate.”

But the Sons of Confederate Veterans group argues that the flag also represents a kind of regional pride that is not bound by race. It has won the backing of some civil liberties groups which argue that the license plate qualifies for free speech protection under the Constitution’s First Amendment.

The case is yet another reminder that despite the century and a half since the Civil War, the legacy of slavery still haunts this country.